1. Field of the Invention
The present invention relates to a machinery sound absorbing apparatus, and more particularly, to a machinery sound absorbing apparatus which can absorb machinery sound generated from a large-sized machine such as a power press and a metal cutting machine.
2. Description of the Related Art
A plurality of large-sized machines are arranged in a factory. Such machines are generating sources of machinery sound. In this case, it is desirable to avoid that the machinery sound is generated from the plurality of generating sources at the same time. Especially, it is desirable to absorb a large volume of machinery sound generated from the large-sized machine such as a power press, a metal cutting machine, and an injection molding machine.
It is well known to provide a machinery sound absorbing board. As the machinery sound absorbing board, there are known various boards such as a wave-shaped plate, a wall board having a lot of projections, and a machinery sound absorbing board having a porous surface. These boards are provided for the generating source of the machinery sound whose position is not defined. When the position of the generating source of the machinery sound is defined, these boards such as a wave-shaped plate, a wall board having a lot of projections, and a machinery sound absorbing board having a porous surface are not the most appropriate.
It is desirable to most appropriately absorb the machinery sound generated from the machinery sound generating source which the position is fixed. Also, it is desirable that a quantity of reflected wave is less.
In conjunction with the above description, a sound absorbing and shielding apparatus is disclosed in Japanese Laid Open Utility Model Application (JPU-A-Showa 57-172499). In this reference, the sound absorbing and shielding apparatus has a substrate (1) and an sound absorbing material (2) connected to the substrate (1) on one side and having a saw-tooth shape on the other side.
Also, an elastic surface wave filter is disclosed in Japanese Laid Open Patent Application (JP-A-Showa 57-127321). In this reference, an input transducer, an output transducer and a sound absorbing film for absorbing an unnecessary wave are provided on a piezo-electric plate. The sound absorbing film has an obliquely deep cutting portion on the back side of the transducer.
Also, a sound absorbing material is disclosed in Japanese Laid Open Utility Model Application (JPU-A-Showa 59-186308). In this reference, a lot of tapered holes are provided on at least one of surfaces of a foamed synthetic resin to have a sharp tip to the inner direction.
Also, a sound absorbing structure is disclosed in Japanese Laid Open Utility Model Application (JPU-A-Showa 63-71211). In this reference, the sound absorbing structure is formed of a water repellent material and a cavity having a cone cross section such that a sound wave entering from an opening portion is absorbed, interfered with each other, and converged and then attenuated.
Also, a sound erasing apparatus is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 9-212175). In this reference, a sound passes through a position on a propagation path and a reflection of the sound also passes through the position. The sound and the reflection are interfered with each other by use of a phase difference between them to attenuate them. A structure (2) has a curved surface which is formed from a part of a spherical surface, as a part of an internal closed space. A sound input section (3) has a terminate (6) on a center position P0 of the sphere in the structure (2).
Also, a fluid circulated tank is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 10-9999). In this reference, a sound absorbing room (2) is provided at a corner section (1e) of a fluid circulated tank (1) and is filled with the same fluid as the tank (1). An interface between the tank (1) and the sound absorbing room (2) is formed of sound transmitting material (2a). The inside of the sound absorbing room (2) is separated by sound absorbing material (2b), and the inside surface of the sound absorbing room (2) is covered with a saw-tooth shaped sound absorbing material (2c).